THE IMMUNE SYSTEM

BY: JEDI MASTER HARRISON

NONSPECIFIC MECHANISMS (general barriers to infection)• LAYERS OF DEFENSE:

• SKIN

• MUCOUS MEMBRANE

• INTERACTING MECHANISMS

• PHAGOCYTOSIS

• ANTIMICROBIAL PROTEINS

• THE INFLAMMATORY RESPONSE

THE BODY’S DEFENSE SYSTEM

FIRST LINE OF DEFENSE

SECOND LINE OF DEFENSE

SKINTHE SKIN COVERS THE ENTIRE BODY

◘ It can’t normally be penetrated by bacteria or viruses◘ Cuts or abrasions can allow potentially harmful bacteria or

viruses to enter the body.

THE SKIN IS LIKE A FORCE FIELD AROUND THE BODY. IT KEEPS UNWANTED INVADERS

OUT!

• Lines the digestive, respiratory and genitourinary tracts

• Bars entry of harmful microbes

• Also counters pathogens with chemical defenses

*saliva, tears, and mucous secretions bathe the surface of exposed epithelia washing away many potential invaders

EX: LYSOZYME- an enzyme that digest the cell walls of many bacteria and destroys many microbes entering the upper respiratory system and the openings around the eyes.

MUCOUS MEMBRANE

IT’S LIKE PERSONAL SHIELDS FOR YOUR LUNGS, INTESTINES, AND THE GENITOURINARY TRACT.

PERSONAL SHIELDS

EXAMPLES OF THE MUCOUS MEMBRANE AT WORK:

• Mucus: the viscous fluid secreted by cells of the mucous membranes; it traps particles that contact it.

• Lining the trachea are specialized epithelial cells equipped with cilia that sweep out microbes and other particles trapped by the mucus, which keeps them from entering the lungs.

• If microbes in food or that are trapped in mucus are swallowed, it must pass through the highly acidic gastric juice produced by the stomach lining. This destroys most of the microbes before they can enter the intestinal tract.

MUCOUS MEMBRANE AT WORK

Internal defense mechanisms that are nonspecific depend mainly on PHAGOCYTOSIS:* PHAGOCYTOSIS is the ingestion of invading particles by certain types of white blood cells *

THE SECOND LINE OF DEFENSE

• Neutrophils comprise about 60% to 70% of all white blood cells• Attracted by chemical signals, neutrophils can leave the blood and enter infected tissue by

amoeboid movement.• Once there they can DESTROY the microbes!!!

(this migration of a chemical attractant is called chemotaxis)

**Neutrophils tend to self-destruct as they destroy foreign invaders so they’re average life is only about a few days.

• Monocytes (only make up about 5% of the WBC) strengthen phagocytic defense

•Monocytes mature into MACROPHAGES

Neutrophils are like SUICIDE BOMBERS!

Macrophages continued on next slide

MACROPHAGES: The largest phagocytic cells

THE SECOND LINE OF DEFENSE

• Macrophages are amoeboid cells that move through tissue fibers and engulf and digest cellular debris and pathogens by phagocytosis

• They also stimulate lymphocytes and other immune cells to respond to pathogens• A majority of macrophages are stationed at strategic points where microbial invasion is

likely to occur (LIKE A BLOCKADE)• Fixed macrophages are especially numerous in the lymph nodes and in the spleen,

which are key organs of the lymphatic system.

BLOCKADE OF NABOO

• About 1.5% of the white cells

• Their defend against larger parasitic invaders such as worms

• Don’t attack microorganisms directly

• Destroy the body’s own infected cells, especially cells harboring viruses

• Also attack cells that could form tumors

• The attack is not by phagocytosis but an attack on the membrane of the target cell

• This causes the cell to break open

EOSINOPHILS

NATURAL KILLER CELLS

• The most important antimicrobial proteins in the blood and tissues are interferons and the complement system.

• INTERFERONS: proteins secreted by virus-infected cells that inhibit neighboring cells from making new viruses

• COMPLEMENT PROTEINS: involved in nonspecific and specific defense

• Can lyse a cell target by combining with antibodies

• A local inflammatory response is triggered by tissue damage. Injured cells release histamine, a chemical signal that dilates blood vessels and increases capillary permeability allowing large numbers of phagocytic white blood cells to enter the interstitial fluid.

ANTIMICROBIAL PROTEINS

• The immune system recognizes foreign microbes, toxins or transplanted tissues

• It knows that they don’t belong

• It then develops an immune response to inactivate or destroy the specific type of invader

ANTIGEN: a foreign substance that elicits an immune response

• Most antigens are proteins or large polysaccharides

• Antigens that trigger an immune response include molecules belonging to viruses, bacteria, fungi, protozoa, and parasitic worms.

ANTIBODIES: specialized lymphocytes that defend the body against one specific type of antigen.

• Antibodies make up a class of proteins called immunoglobulins

• An antibody does not usually destroy an antigen directly but targets it for elimination by complement or phagocytes

SPECIFIC DEFENDERS

IMMUNITY• Immunity is the result of the immune system’s enhanced response to a previously

encountered pathogen.

ACTIVE IMMUNITY: acquired by exposure to an actual disease or to a vaccine that simulates a disease.

PASSIVE IMMUNITY: acquired by administering antibodies formed in others, or it can be

passed from mother to child via the placenta and milk.

HUMORAL IMMUNITY: based on circulation of antibodies in the blood and lymph, and defends against free viruses, bacteria, and other extracellular threats.

CELL-MEDIATED IMMUNITY: reacts against transplanted tissue and cancer cells.

IT’S NOT A JOKE!

TWO MAIN FUNCTIONAL BRANCHES OF IMMUNITY

LYMPHOCYTES=MAIN CELLS OF THE IMMUNE SYSTEM

LYMPHOCYTES:

• Originate in bone marrow

B LYMPHOCYTES: mature in the bone marrow and function in humoral immunity.

• B cells defend against pathogens in body fluids by generating specific antibodies

T LYMPHOCYTES: mature in the thymus and function mainly in cell-mediated immunity.

• T cells defend against intracellular pathogens

CLONAL SELECTION OF LYMPHOCYTES• Is the cellular basis for immunological specificity and diversity

• Each lymphocyte recognizes and responds to only one antigen

• There is an enormous diversity of antigen-specific lymphocytes.

• This allows the immune system to defend against an almost unlimited variety of antigens

HOW IT WORKS:

• Each lymphocytes’ specificity for an antigenic target is predetermined during embryonic development (before an encounter with an antigen ever takes place)

• The mark of this specificity is the antigen receptor the lymphocyte bears on its surface

• If that antigen enters the body and binds to receptors on the specific lymphocytes, then those lymphocytes are activated to mount an attack (immune response)

• The selected cells go through cell division and develop into a large number of a clone of cells that combats the antigen that initiated the response.

CLONE TROOPERSDON’T HAVE TO WRITE

CELL MEMORY OF IMMUNITY• Upon first exposure to an antigen lymphocytes go through PRIMARY IMMUNE RESPONSE

PRIMARY IMMUNE RESPONSE: between initial exposure to an antigen and maximum production of effector cells, there is a lag period of 5 to 10 days. During this lag period, the lymphocytes selected by the antigen are differentiating into effector T cells and antibody-producing plasma cells.

• If the body is exposed to the same antigen at some time later, the response is faster (only 3 to 5 days) and more prolonged than the primary response.

SECONDARY IMMUNE RESPONSE: the antibodies produced at this time are also more effective in binding to the antigen than those produced during the primary response.

IMMUNOLOGICAL MEMORY: The immune system’s ability to recognize an antigen that it already encountered

• IMMUNOLOGICAL MEMORY is possible due to MEMORY CELLS

MEMORY CELLS• MEMORY CELLS are produced along with the relatively short-lived effector cells of the

primary immune response.

• During the primary response, memory cells are inactive

• Survive for long periods of time

• Multiply rapidly when exposed again to the same antigen that caused their formation

Memory cells are responsible for the usual lifelong immunity of chickenpox after childhood exposure

MOLECULAR MARKERS

• Molecular markers on cell surfaces function in self/nonself recognition

SELF-TOLERANCE: develops as T and B lymphocytes bearing antigen receptors mature in the thymus and bone marrow, and continues to develop even as the cells migrate to lymphoid tissues.

• Any lymphocytes with receptors for molecules present in the body are destroyed or are made nonfunctional

• This leaves only lymphocytes that are reactive against foreign molecules

MAJOR HISTOCOMPATIBILITY COMPLEX (MHC): a biochemical fingerprint unique to each individual

2 TYPES OF MHC:

• CLASS I MHC: LOCATED ON ALL NUCLEATED CELLS (ALMOST EVERY CELL IN THE BODY)

• CLASS II MHC: RESTRICTED TO A FEW SPECIALIZED CELL TYPES OF THE BODY’S DEFENSE SYSTEM (MACROPHAGES, B CELLS, AND ACTIVATED T CELLS)

DISEASES CAUSED BY ABNORMALITIES IN IMMUNE FUNCTION• Sometimes the immune system screws up and turns against itself

• This can lead to autoimmune diseases such as:

• Rheumatoid arthritis

• Insulin-dependent diabetesOr in allergies such as:

• Hay fever (histamine is released from mast cells by the allergen pollen)

Some people are naturally deficient in humoral or cell-mediated immune defenses, or both.• AIDS is caused by the destruction of CD4-bearing T cells and other cells by HIV, the

human immunodeficiency virus, over a period of years• AIDS is marked by a low level of helper T cells and

OVERVIEW SKIN

MUCOUS MEMBRANE

MACROPHAGES

ANTIGENS

ANTIBODIES

MEMORY CELLS

MOLECULAR MARKERS